The invention relates to a cannula system of the species defined in the preamble of claim 1 and used to insert a catheter into biological tissue or the like.
A cannula system is known from the European patent document A2 0,567,321 with which to insert a catheter into biological tissue and which comprises a steel cannula with a sharp front tip and a rear end where the cannula is affixed to a plastic fitting. Moreover the known cannula system comprises a plastic housing having a front aperture at its front end and a rear aperture at its rear end as seen in the direction of piercing. The fitting is held against the housing between an advanced position wherein the front end of the cannula axially projects beyond the housing, and a retracted position wherein the cannula is received in this housing and is displaceable in the axial cannular direction.
The known cannula system is used with a thin tube fitted with projection enclosing the cannula and allowing detachably connecting the tube to the housing of the cannula system.
In order to introduce a catheter into biological tissue, for instance the body of a patient using the cannula system, the cannula will be in its advanced position wherein the sharp tip projects beyond the housing and the front end of the tube in the direction of piercing, whereby it is possible then to insert the cannula into the skin of the patient and to insert the thin tube into the patient""s body through the puncture.
After tube insertion, the user moves the fitting together with the cannula into the retracted position wherein the cannula is received in the housing and separates the housing from the tube. The sole purpose of moving the cannula into its retracted position is to prevent contact with the sharp cannula tip and hence any consequent injury and infections.
Infusion may be immediately carried out through the tube remaining in the patient""s body or a flexible catheter may be inserted into the patient""s body to infuse liquids into this body or to remove them from it.
One drawback of the known cannula system is that following tube insertion, the cannula system must be detached from the tube before a flexible feed hose can be attached to the tube. This feature entails further operational steps making handling more complex.
The PCT document US95/05,672 discloses a cannula system of the cited kind wherein the catheter is firmly affixed to the front end of the housing at which it terminates. In the retracted position of the slider, the cannula remains by its front end in the catheter and in this manner sets up fluid communication between the catheter and the hollow inside of the slider, this slider being fitted at its rear end with a hose adapter.
This known cannula system incurs the drawback of mandatorily requiring open-tip catheters and precludes closed-tip catheters and multi-duct catheters. Furthermore the system entails a large dead space and raises sealing difficulties.
The WO 95/20,991 patent document discloses a system for using micro-dialysis probes wherein the microdialysis probe first is seated in a cannula fitted with a longitudinal slot and this sub-assembly then is made to pierce the tissue. Once the microdialysis catheter is present in the tissue, the cannula is withdrawn and is separated through the slot from the fluid duct of the microdialysis catheter.
The patent document WO 96/25,088 discloses a device for using sensors which also requires a slitted needle which, subsequent to sensor application, can be separated form the sensor.
Because of the slitted cannula, both known systems entail complex manufacture and impractical operation.
The objective of the invention is to create a cannula system of the above cited kind which shall be suitable for closed-tip catheters and for multi-duct catheters, for instance for microdialysis catheters known from the German patent document A1 197 14 572 or German patent 33 41 170, and which shall be fully sealed.
The basic concept of the disclosure of the present invention is to guide the catheter through the slider and the housing as far as the rear housing end and to affix the catheter in a direction opposite the direction of puncturing, where the catheter can be directly connected to hoses. The catheter continues in especially advantageous manner beyond the rear housing end. Sealing is assured everywhere.
The catheter being affixed to the housing and/or the slider only in the direction opposite that of puncturing, it cannot be accidentally pulled rearward out of the housing, while at the same time it is possible to advance it in the direction of puncturing after such piercing arbitrarily far beyond the cannula tip. When the catheter is affixed to the slider in the direction of puncturing, the cannula may be left prior to use in its retracted position wherein its tip is protected. The slider will be advanced prior to use and the catheter will be driven along.
However the catheter also may be wholly rigidly joined to the rear housing end, in which case it runs as far as the cannula tip when this cannula is in its advanced position.
While it is basically possible to keep the slider manually in position relative to the housing as the cannula is inserted, an appropriate embodiment of the invention makes use of locking means to lock the slider to the housing at least in the advanced slider position. Piercing may then be implemented solely by holding the housing. Thereafter unlocking, ie disengagement may be implemented and the slider may be retracted. For that purpose one embodiment of the invention provides means for manually retracting the cannula. Advantageously the housing comprises a slot running in the direction of displacement of the cannula and crossed by a radial protrusion of the slider. The slider can be forced back by means of the said externally accessible protrusion.
In one embodiment of the invention, the slider comprises a two-arm lever pivoting about an axis transversely to its sliding direction, the front lever arm in the front limit position of the slider engaging from behind an edge at the front end of the housing and this lever being disengaged, that is unlocked, by pressing on the front lever arm. Accordingly the two-arm lever is an actuator both to disengage and lock and to displace the slider.
A spring is provided in an especially appropriate embodiment of the invention to load the slider in the direction of its rear limit position, the slider being kept in its front limit position by an externally disengageable catch. In this embodiment the spring implements the return motion of the slider and cannula, thus facilitating handling.
When using a spring, the catch appropriately comprises a hook which is connected to the slider and which in the front limit position of the slider engages behind an edge at the front end of the housing and which is yielding in the disengaging direction. This basic design of the catch allows a further development in which the hook is fitted with a protrusion projecting beyond the front housing end in such manner that upon the cannula puncturing by the cannula, the protrusion hits the tissue surface and unlocks the hook. In this embodiment cannula retraction practically is automatic and no particular attention need be paid to disengagement and retraction.
The disengaging means may be designed in a number of ways and the minimum distance between an obstacle and that housing which when reached shall cause the disengaging means to unlock can be selected within wide limits. In an appropriate further development of the invention comprising the locking means, these are fitted with a locking blade connected to the adapter and which in the locking position elastically enters a radial clearance inside the housing, the disengaging means comprising an axially displaceable disengaging element of which the front end projects radially beyond the front end of the housing and of which the rear end comprises a disengaging blade extending inside the housing and upon axial displacement of the disengaging element engages underneath the locking blade in the direction of the housing and moves out of the clearance. This design allows simple and economical manufacture and operates reliable.
In a further development of the above embodiment, the disengaging blade and the locking blade when at rest abut each other by means of bevels in such manner that upon axial displacement of the disengaging element the disengaging blade lifts the locking blade toward the housing. This design offers simple and economical manufacture.
In a further development of the embodiment comprising a disengaging blade and a locking blade, at least two disengaging blades and associated locking blades are present at diametrically opposite sites of the disengaging element or slider relative to the cannula. This embodiment prevents the disengaging element is prevented from being bent and the reliability of the disengaging means is improved.
In a further development of the embodiment comprising the disengaging element, its front end is substantially annular. In this manner reliable disengagement upon impact by the disengaging element on an obstacle is assured regardless of the angular position of the housing about the cannula axis.
In another embodiment of the invention, the spring is helical, in particular it is a compression spring coaxial with the cannula, and is mounted between the housing and the adapter. This embodiment is particular simple and economical in manufacture. By appropriately dimensioning the compression spring, the force acting on the slider toward the retracted position after disengagement will be selectable.
Another embodiment comprises retention means to hold the housing against a body surface, for instance the skin of a human. In this embodiment, following inserting the cannula cannula and moving it into its retracted position, the cannula system is held for instance on the skin of a human in such manner that stressing the catheter by the weight of remnant cannula system on the catheter shall be prevented.
In a further development of the embodiment comprising retention means, these adapters are fitted on the housing outside using adhesive means, in particular an adhesive strip. In this embodiment the housing adheres to the skin and can be subsequently removed from it, for instance as the catheter is removed from the patient""s body.
Appropriately the housing comprises a substantially flattened surface to rest on the body surface, for instance the skin of a human. In this design the housing rests in substantially two-dimensional manner on the skin and as a result pressure points or the like are precluded from the skin.
Lastly in another embodiment of the invention, the front aperture of the housing comprises a free inside width substantially corresponding to the outside diameter of the cannula. In this embodiment the cannula is laterally guided into its advanced position on one hand, whereby sideways slippage of the cannula is averted during puncturing. On the other hand when the cannula has been retracted, the catheter will be guided in the front aperture of the cannula system. This design averts damages that might arise when a flexible catheter is bent immediately behind the cannula tip and away from latter and thereby would rest by its outside surface against the cannula tip.